The present invention relates to vibration control systems and, more particularly, to a system and method for seamlessly controlling the stiffness and damping of a liquid spring vibration control system using a controlled valve.
Vibration is a destructive force in a variety of environments. Vibration can be periodic, as created by a rotating compressor in an air conditioning unit or an engine in a car. Periodic vibration is characterized by a particular frequency and amplitude. Random vibration, on the other hand, has no dominant frequency and no dominant amplitude. Instead, the vibration must be analyzed quantitatively to determine average amplitudes and common frequencies. Damping is the process by which vibration steadily diminishes in amplitude. In damping, the energy of the vibrating system is dissipated as friction or heat, or transmitted as sound. The process of damping can take any of several forms, and often more than one form is present.
Liquid springs can utilize a compressible liquid to provide damping forces. A liquid spring can comprise a cylindrical housing having an internal chamber with a compressible liquid therein, a piston reciprocally disposed in the chamber, and a rod structure axially movable into and out of the chamber, secured to the piston, and having an outer longitudinal portion projecting outwardly of one of the housing ends. If a liquid spring is used between a vehicle frame and an associated wheel support structure, the compressible liquid within the liquid spring generates both stiffness and damping forces in the suspension system in response to relative axial translation between the rod structure and housing of the liquid spring caused by relative displacement between the wheel and the frame.
Although liquid springs provide stiffness or damping forces, a need exists for a way to change the amount of stiffness or damping of the liquid spring in response to changing conditions.
The present invention in an exemplary embodiment is a vibration control system for a structure having a first structural member and a second structural member. A vibration control system according to an embodiment has a liquid spring operably interposed between the first structural member and the second structural member using a compressible liquid to generate spring forces in response to relative displacement between the first structural member and the second structural member. The present invention provides for a system and method of changing the stiffness of a vibration control system in response to changing conditions.
The present invention in one embodiment is an application for a suspension system for use on a vehicle having a frame and a wheel structure. The system has a liquid spring operably interposed between the frame and the wheel structure. The liquid spring uses a compressible liquid to generate spring forces in the suspension system in response to relative displacement between the frame and the wheel structure. A second volume of compressible liquid is stored in a second chamber. The second volume is removably connected to the liquid spring by a fluid passage. A valve is coupled to the fluid passage. The valve is selectively operable to place the second volume in communication with the liquid spring. A controller is electrically coupled to the valve, the controller emitting a control signal having a period and a pulse width to control the valve. The controller alters the pulse width of the control signal to open and close the valve for a portion of the period.
In an embodiment of the present invention, a height sensor is electrically coupled to the controller. The height sensor produces a signal indicative of the position of the frame in relation to the wheel. A speed sensor is electrically coupled to the controller. The speed sensor produces a signal indicative of the speed of the vehicle. A steering position sensor is electrically coupled to the controller. The steering position sensor produces a signal indicative of a steering wheel position for the vehicle. The controller alters the pulse width of the control signal in response to at least one of the group consisting of the height sensor signal, the speed sensor signal, and the steering wheel position signal.
In an additional embodiment, an accelerometer is electrically coupled to the controller. The accelerometer produces a signal indicative of an acceleration experienced by the vehicle. The controller may also alter the pulse width of the control signal in response to the accelerometer signal. In yet another embodiment, a brake sensor is electrically coupled to the controller. The brake sensor produces a signal indicative of a brake application of the vehicle. The controller may also alter the pulse width of the control signal in response to the brake sensor signal.
In an additional embodiment, a mode selection switch is electrically coupled to the controller. The mode selection switch producing a signal indicative of desired suspension performance. In an embodiment, the selection switch allows for the selection of three settings of varying ride and handling character. The controller may further alter the pulse width in response to the mode selection switch signal.
In an embodiment of the present invention, the suspension system is for a vehicle with a plurality of wheels. Each of the wheels has at least one liquid spring. Each wheel also has an associated height sensor. The controller alters the pulse width for each wheel in response to the particular wheel""s height sensor signal, the speed sensor signal, the steering wheel position signal, and the mode selection switch signal. In an exemplary embodiment, the vehicle has four wheels, four liquid springs, and four height sensors.
In an embodiment, the control signal has a period of about one second and the pulse width may be modulated to activate the valve for any portion of the period.